Emulsion coating system



" Jam. 2, 196s E. J. KING 3,361,109

EMULSION COATING SYSTEM Filed Jan. 7, 1966 2 Sheets-Sheet 1 Jan. 2, 1968E. J. KING EMULSION COATING SYSTEM 2 Sheets-Sheet 2 Filed Jan.

United States Patent 3,361,109 EMULSIUN COATING SYSTEM Ellwood J. King,Newbury Park, Calif., assignor to Minnesota Mining and ManufacturingCompany, St. Paul, Minn., a corporation of Delaware Filed Jan. 7, 1966,Ser. No. 519,315 11 Claims. (Cl. 118-209) ABSTRACT 0F THE DISCLOSURE Thepresent invention relates to an apparatus for producing a uniformcoating of coating material on the surface of a substantially planarsubstrate using a dispensing apparatus for dispensing the coatingmaterial toward a means for distributing the coating material on thesubstantially planar substrate. The means for distributing the coatingmaterial has a curved bottom structure lying on and contacting thesurface of the substrate and includes an opening through the means fordistributing the coating material to allow the coating material to fiowthrough the opening and onto the surface of the substantially planarsubstrate. In one embodiment of the invention, the means fordistributing -is a spherical shell and in the second embodiment themeans for distributing is a trough-shaped member. In both embodimentsthe opening is preferably away from the area of contact between thecurved bottom and the surface of the substrate so as to allow for thecoating material to ow to the surface of the substrate. When theapparatus of the present invention is used to coat a disc member, thedisc is rotated and the distributing means is moved in a radialdirection along the surface of the disc as the disc is rotated. In orderto insure a uniform coating of the coating material, either the rotationof the disc -is variable or the radial movement of the distributingmeans is variable so as to produce a uniform area loading on the disc.

This invention relates to an apparatus for producing a coating of amaterial, such as an emulsion material, on a substrate. The shape of thesubstrate is not limited to any particular conguration and may havevarying configurations such as a disc, tape or plate. In particular, thepresent invention relates to an apparatus for producing a very thinuniform coating of the emulsion material on the substrate. Specifically,the present invention relates to an apparatus for producing a coating ofthe emulsion material on the substrate wherein the coated substrate maybe used as a recording medium in a high-resolution recording system.

The emulsions which may be coated by the apparatus of the presentinvention generally are considered to be of the photographic type.Although the emulsions are generally characterized as of thephotographic type, this does not mean that the emulsions may be exposedonly by the use of visible light energy. For example, the recording ofinformation on the emulsion coating on the substrate may be produced bysensitizing the emulsion for exposure by energy having wavelengths otherthan the visible band. For example, the use of infrared or ultravioletenergy may be used to expose a properly sensitized emulsion, and aparticularly useful means of exposing the emulsion material is the useof an electron beam. The use of an electron beam for recording hascertain advantages, since it is relatively easy to modulate and controlthe electron beam when compared with other types of energy such asvisible light. One difficulty with the use of electron beam recording isthat the recording must take place within a partial vacuum. Therecording within a partial vacuum gives rise to a relatively complexrecording structure and, in addition, requires that the emulsionmaterial is iirmly adhering to the surface of the substrate.

One specic example of a high-resolution recording system uses asubstrate having a disc shape which has been coated by the coatingapparatus of the present invention with the emulsion material.Information may be recorded on the coated disc by rotating the disc andby exposing progressive portions of the emulsion coating the disc alonga spiral path in accordance with the information. The exposing of theprogressive portions of the emulsion material in accordance with theinformation may be accomplished by directing an electron beam toward therotating coated disc and by modulating the electron beam with theinformation. The spiral path of the recorded information on the surfaceof the coated disc may be produced by either moving the disc whilerotating relative to the position of the electron beam or by moving theelectron beam relative to the rotating disc or by producing a deflectionof the electron beam in a radial path as the disc rotates,

After the emulsion material on the coated disc has been exposed at theprogressive portions along the spiral path, the emulsion material isdeveloped in a normal photographic manner to produce translucent andopaque areas on the surface of the disc in accordance with theinformation. The translucent and opaque portions of the developedemulsion material may now be used to reproduce the recorded informationusing optical techniques. In addition, if it is desired to producecopies of the original` recording, the copies may be produced from theoriginal recording by normal photographic means such as by the use of acontact print or by projection methods.

In order to obtain the maximum density and resolution of the informationrecorded on the disc, the spot size of the electron beam is maintainedas small as possible and an emulsion material is used which has a grainwhich is ultrafine. In addition, it is desirable to maintain a very thinuniform coating of the emulsion material on the substrate. The use of avery thin uniform coating of emulsion material helps to lower the effectof the emulsion material on the electron beam during the recording ofthe information and on the light beam during the reproduction of theinformation. Specifically, the uniformity of the coating helps toeliminate any effects in the recording and reproduction due tovariations of thickness on the different beams of energy. Also,maintaining a very thin coating of the emulsion material reduces thespreading effect of the emulsion material on the various beams of energyused in recording and reproducing and helps to maintain ahigh-resolution recording of the information.

It is to be appreciated that the above method of exposing the `emulsionmaterial coated on the substrate is illustrative only and that properlysensitized emulsion material may also be exposed by other forms ofenergy such as visible light or infrared or ultraviolet energy. Priorart apparatus for coating emulsion material has not been able to producethe desired very thin uniform coating of emulsion material onthesubstrate. It has, therefore, been difficult to use substrates, ascoated by the prior art apparatus, as a recording medium inhighresolution recording systems. The present invention is directed toan apparatus for Coating a substrate, such as a disc, plate or tape,with an emulsion material so that the coating of emulsion materialacross the surface of the substrate is very thin and uniform.

The emulsion material is applied to the surface of the substrate in awet state, but the present invention applies the emulsion material in anextremely uniform manner and controls the thickness of the emulsionmaterial in the wet state to a desired value. As the emulsion materialdries, it shrinks to significantly reduce the thickness of the emulsionmaterial. However, the relationship of the wet to dry state of theemulsion material follows a constant pattern which may be reproduced insucceding coatings with a high degree of accuracy.

As an example, the emulsion material may have a relationship of itsthickness from the wet to diy state by a constant factor such as afactor of 38. rfhis would mean that the emulsion material as applied bythe apparatus of the present invention to the surface of the substrateshrinks by a factor of 38 times from its wet to dry thickness. As aspecific example, the deposition of a wet lm of emulsion material of athickness of 0.0075 inch produces a dry film of emulsion material of athickness of approximately 0.0002 inch, which is approximately 5 micronsthick.

Although the use of a S-micron layer of emulsion material on the surfaceof a substrate produces excellent results when information is recordedby progressively exposing the emulsion material, the apparatus of thepresent invention can produce coatings of emulsion material on thesurface of a Isubstrate having dry thicknesses thinner or thicker than 5microns. Specifically, the apparatus of the present invention produces acoating of an emulsion material on the surface of a substrate whereinthe emulsion material has a high degree of uniformity across the surfaceof the substrate and wherein the em-ulsion material has a controlledthickness which may be quite small in comparison to prior art emulsioncoatings.

The present invention generally produces the uniform coating of theemulsion material by first maintaining a controlled flow of emulsionmaterial from a dispensing apparatus. The emulsion material flows into ameans for providing a uniform distribution of the emulsion materialacross local areas of the surface of a substrate. The dispensingapparatus and distribution means provide a coating station and thesubstrate is moved relative to the coating :station to produce a uniformcoating of emulsion material across the surface of the substrate. Inorder to control the uniformity and thickness of the coating of theemulsion material, the present invention maintains very close control ofthree particular operating conditions. These conditions are: First, theflow rate of the emulsion material from the dispensing apparatus must beaccurately maintained. Second, the velocity of the substrate which isbeing coated relative to the coating station must be accuratelycontrolled. Third, and most important, means must be provided forproducing a high degree of distribution uniformity across at least localareas of the substrate.

Maintaining a control over the flow rate of the emulsion from thedispensing apparatus is generally not a diicut problem. For example, aglass separatory funnel may be suspended over the substrate and the rateof flow of emulsion material from the funnel may be easily controlled bya value structure. This type of funnel and value structure is corrunonin laboratory use. The valve structure is generally set to produce aconstant rate of flow of emulsion material. The rate of flow isgenerally measured in drops per second. It may be desirable sometimes tocontrol the setting of the valve structure s0 as to produce anon-uniform rate of ow of emulsion material.

The control of the relative velocity `of the substrate in relation tothe coating station is again not a particularly diicult problem. Forexample, if the substrate is a tape which is moving on a longitudinaldirection, the tape may be maintained at a constant velocity by acapstan drive system. The coating station, for example, may be suspendedover the tape and when the tape is moved at a constant velocity, ofcourse, the relative velocity between the coating station and the tapeis maintained at a constant value.

The maintenance of the constant velocity between the substrate and thecoating station does present problems when coating a substrate which hasthe shape of a disc. The coating of the emulsion material on the discmay be accomplished by suspending the coating station above the disc asthe disc rotates and by then moving the coating station radially so asto produce a spiral path between the coating station and the rotatingdisc. When the rotation of the disc is maintained at a vconstant rate,then the velocity between the coaing station and the disc varies inacordance with the radial position between the coating station and thedisc. When the rate of ow of emulsion material from the `dispensingapparatus is maintained at a constant rate, then the unit area loadingof the emulsion material on the surface of the disc would vary inaccordance with the radial position between the coating station and thedisc.

The varying of the unit area loading of the emulsion material on thesurface of the disc would produce a nonunform layer of emulsionmaterial. The non-uniformity of the thickness of the emulsion materialon the surface of the disc may be corrected in various Ways. Forexample, one embodiment of the invention corrects for the non-uniformityof the thickness of emulsion material by varying the spacing betweenadjacent turns `along the spiral path produced by the relativerotational and radial movement between the coating station and the disc.The variation of the spacing of the turns along the spiral path isdesigned so that the unit area loading of the emulsion material on thesurface of the disc is constant at all points along the spiral path ofthe coating station relative to the disc. Another embodiment of theinvention corrects for the non-uniformity of the thickness of theemulsion layer by varying the rotational rate of the disc so as toproduce a constant velocity between the coating station and the disc andto achieve a constant unit area loading of the emulsion material. Athird method which may be used to correct for the non-uniformity of thethickness of the emulsion material would be to regulate the rate of flowof emulsion material from the dispensing apparatus so as to produce aconstant unit area loading of the emulsion material on the rotatingdisc.

The third condition for producing a uniform thin emulsion coating on thesurface of the substrate is in the use of a means for assuring a highdegree of uniform distribution of the emulsion material across localareas of the surface of the substrate. Prior art methods do not spreadthe emulsion material evenly over the surface of the substrate. Forexample, if the dispensing apparatus would merely drop the emulsionmaterial on the surface of the substrate, this would produce an uneventhickness of the emulsion material on the surface of the substrate dueto the periodic dropping of the emulsion material. The emulsion materialdoes not have the consistency to cornpletely spread out evenly over thesurface of the substrate, but rather tends to stay lumped up at placeswhere the drops of emulsion material fall on the surface of thesubstrate. Prior art methods of leveling the coating of emulsionm-aterial which use such means as brushes, Scrapers, etc., producecoatings which are adequate for normal photographic purposes, but whichwould be inadequate for use in a high-resolution recording system.Moreover, due to the desirability of maintaining a very thin coating ofemulsion material on the surface of the substrate, any non-uniformity inthe very thin coating has a relatively larger effect than with a thickercoating. For example, a 2-micron variation in a S-micron coating is a40% variation, whereas a 2-micron variation in a 100- micron coating isonly a 2% variation.

The present invention, therefore, incorporates novel means to uniformlydistribute the emulsion material on the surface of the substrate and, inaddition, to act as a hydraulic lter so as to smooth out the flow of theemulsion material from the dispensing apparatus. For example, when theapparatus of the present invention is used for coating a disc, an upperchamber is lled with emulsion material and is supported over the disc.As mentioned above, a valve arrangement controls the rate of flow of theemulsion material from the dispensing apparatus at a particular value. Alight spherical shell is supported under and moves with the dispensingapparatus to continuously receive the flow and store a small amount ofthe emulsion material from the dispensing tank. The light sphericalshell is arranged so that it lightly rests on the surface of the discand it is attached to the same support as the dispensing apparatus sothat a xed relationship is achieved between the dispensing apparatus andthe spherical shell. A small opening in the bottom of the lightspherical shell extends from the inside of the shell to the bottomsurface and the opening is off-center from the point of contact betweenthe surface of the disc an-d the spherical shell to allow emulsionmaterial to drain onto the surface of the disc.

The emulsion material which drains through the opening in the sphericalshell forms a smooth meniscus ring approximately centered about thecontact point between the disc and the spherical shell. The size of theopening in the spherical shell is selected so as to produce a particularthickness of the emulsion material on the surface of the disc and tomaintain a desired head of emulsion material in the spherical shell whenthe rate of flow of emulsion material from the dispensing apparatus isset at a desired value and taking into account the relative velocitybetween the spherical shell and the rotating disc. Although the flowcharacteristics from the dispensing apparatus are periodic, for example,2 drops of emulsion material per second, the llow characteristics fromthe bottom of the spherical shell to the surface of the disc are Verysmooth and uniform. The spherical shell, therefore, acts as a hydrauliclilter to smoothout llow irregularities from the dispensing tank. Inaddition, the flow of the emulsion material through the opening in thespherical shell wets the area as dened by a meniscus ring around thecontact point between the spherical shell and the disc so as touniformly distribute the emulsion material across a local area of thedisc. The spherical shell, therefore, uniformly distributes the emulsionmaterial to the surface of the disc and produces a uniform coatingacross the entire surface of the disc after the spherical shell makes acomplete spiral path.

When the apparatus of the present invention is used to produce a coatingof emulsion material on the surface of a substrate such as a plate or atape, the means for uniformly distributing the emulsion material to thesurface of the substrate is a trough having a cylindrical bottomsurface. When used to produce a thin uniform coating of emulsionmaterial on a tape, the trough sits across and contacts the tape along aline. The trough may be maintained in a stationary position while thetape is moved underneath the trough using conventional means such as acapstan drive. One or more dispensing apparatuses are supported abovethe trough and dispense a llow of emulsion material into the trough. Thetrough has a slit opening which extends from the inside of the trough tothe bottom surface of the trough, and the slit opening is substantiallyparallel to the contact line between the bottom of the trough and thetape.

The slit opening in the trough allows the emulsion material to drainonto the surface of the tape, and, in addition, allows the emulsionmaterial to form a meniscus along the cylindrical 'bottom surface of thetrough to evenly distribute the emulsion material across the tape as thetape moves relatively to the trough. As with the spherical shell, thetrough contains a head of emulsion material so that the trough acts as ahydraulic filter to smooth out the irregular flow of emulsion materialfrom the dis-` pensing apparatus. Again, the wetting of the cylindricalbottom surface of the trough as defined by the meniscus produces theeven distribution of the emulsion material across the tape.

A clearer understanding of the invention will be had with reference tothe drawings, wherein:

FIGURE 1 is a block diagram of a first embodiment of the invention forproducing a uniform thin coating of emulsion material on the surfrace ofa disc;

FIGURE 2 is a block diagram of a second embodiment of the invention forproducing a uniform thin coating of emulsion material on the surface ofa disc;

FIGURE 3 is a detail view of the spherical shell of either FIGURE 1 orFIGURE 2 and the surface of the disc;

FIGURE 4 is a diagram of a means for removing the spherical shell fromthe surface of the disc without disturbing the uniformity of the coatingof the emulsion material;

FIGURE 5 is a block diagram of an embodiment of the invention forproducing a uniform thin coating of an emulsion material on the surfaceof a tape; and

FIGURE 6 is a detail view of the trough of FIGURE 5 and the surface ofthe tape.

In FIGURE l, a first embodiment of the present invention is shown forproducing a uniform thin coating of an emulsion material on the surfaceof a disc 10. The disc 10 is rotated in a counter-clockwise direction,as shown by an arrow 12, by a motor 14, at a slow rate so thatcentrifugal forces are kept at a low value and do not play any part inthe coating of the surface of the disc 10. The rotation of the disc ltlby the motor 14 is shown schematically in FIGURE 1 and it is to beappreciated that any appropriate method of driving the disc 10 from themotor 14 may be used. A dispensing apparatus 16 having an upper chamber18 is positioned over the disc 10. The upper chamber 18 is lled withemulsion material 20 and the rate of flow of the emulsion material 20from the dispensing apparatus is controlled by a valve 22.

The dispensing apparatus 16 is supported above the disc 10 by upper andlower arm supports 24 and 26. The upper and lower arm supports 24 and 26extend from a rigid .post 28. In addition, a flexible arm 30 extendsfrom the lower arm 26 to support a spherical shell 32. The sphericalshell is positioned under the end of dispensing apparatus 16 to receivethe flow of emulsion material 20 from the dispensing apparatus 16. Thespherical shell 32 rests on the surface of the disc 10 and has a smallopening 34 extending from the inside of the spherical shell to thebottom surface of the spherical shell at a point behind the point ofcontact between the spherical shell 32 and the disc 10.

A cam 3'6 is affixed to the lower end of the post 28 to produce arotation of the post 28 with a rotation of the cam 36. The rotation ofthe post 28 also produces a corresponding rotation of the dispensingtank 16 and spherical shell 32, both of which are connected to the post28. The cam 36 is driven by a wheel 38 which frictionally engages thecam. The wheel is rotated in a clockwise direction, as shown by thearrow 40, by the motor 14. The clockwise rotation of the Wheel 38produces a counter-clockwise rotation of the cam 316 as shown by thearrow 42. The wheel 38 is maintained in contact with the cam 36 throughall positions of the cam by appropriate mechanical means as shownschematically by the spring 44. It is to be noted that although thedriving of the wheel 38 by the motor 14 is shown schematically, anyappropriate mechanical drive means may be used to produce the rotationof the wheel 33.

As the disc 10 is rotated by the motor 14 in the counterclockwisedirection, the dispensing apparatus 1.6 and the spherical shell 32 aremoved in a radial arc across the disc 10'. The valve 22 is adjusted toproduce a flow of emulsion material 2G from the upper chamber 18. Theemulsion material 2G contained in the upper chamber 18 flows through thelower tubing portion of the dispensing apparatus 16 and falls into thespherical shell 32. The emulsion material 20 drains from the sphericalshell 32 through the opening`34 onto the surface of the dise 10. Theemulsion material Ztl spreads out over the bottom surface of thespherical shell 32 and forms a meniscus ring between the spherical shell32 and the surface of the disc l0. The meniscus ring generally has acircular 7 shape surrounding the contact point between the sphericalshell 32 and the surface of the disc 10. Actually, once the emulsionmaterial 20 starts to flow from the opening 34, the spherical shell 32rides on a thin iilm of emulsion material rather than directlycontacting the surface of the disc 16.

As the disc 10 rotates and the spherical shell 32 moves on a radial arc,the flow of emulsion material 20 from the spherical shell 32 forms aspiral path wherein each turn in the spiral path has a relation with thepreceding turn so as to produce a uniform distribution of the emulsionmaterial `across the surface of the disc 10. A partial covering of theemulsion material 46 is shown in FIGURE 1 on the surface of the disc 10.The spherical shell 32 produces the distribution of the emulsionmaterial at localized areas on the surface of the disc 16 by spreadingout the emulsion material and, in addition, the spherical shell 32 actsas a hydraulic filter to smooth out the flow `of the emulsion materialfrom the dispensing apparatus 16. In order for the spherical shell 32 toproperly act as a hydraulic filter, it is desirable to maintain a properhead of emulsion material in the spherical shell.

It is to be appreciated that as the dispensing apparatus 16 and thespherical shell 32 move in a radial arc across the surface of the disc10, the relative velocity between the spherical shell 32 and the disc 10varies in accordance with the particular radial position of thespherical shell. This is assuming that the disc 10 is rotated at aconstant speed as shown in FIGURE 1. Since the time for each revolutionof the disc 10 is constant, the amount of emulsion material fiowing fromthe spherical shell 32 tO the surface of the disc 10 would also beconstant for each revolution of the disc. The constant deposition ofemulsion material for each revolution would produce a non-uniformdistribution of the emulsion material across the surface of the discsince the area to be covered varies with each radial position.

In order to eliminate the non-uniformity of the layer of emulsionmaterial on the disc 10, the cam 36 provides for a variation in thespacing between each adjacent turn along the spiral path of thespherical shell. In this manner, as the spherical shell approaches theinner portion of the disc 10, the spacing between each spiral turnincreases so that the emulsion material has a constant area to cover foreach revolution of the disc 10. The unit area loading `of the disc 10is, therefore, maintained constant so as to eliminate the problem ofnon-uniformity. One problem with the embodiment of FIGURE 1 is that whenthe spacing between adjacent turns along the spiral path of thespherical shell 32 increases as the spherical shell moves in toward thecenter of the disc 10, the emulsion material must, therefore, spreadradially over a larger distance as the spherical shell moves toward thecenter of the disc 10. The additional spreading of the emulsion materialmay be unsatisfactory if the emulsion material does not have thenecessary flow characteristics to spread the emulsion materialuniformly. This problem could be overcome by maintaining an equalspacing between the adjacent turns along the spiral path of thespherical shell Ibut by regulating the flow of the emulsion materialfrom the dispensing apparatus 16 into the shell 32. Another method ofmaintaining a uniform coating of emulsion material on the surface of thedisc 1li, is shown in FIGURE 2.

In FIGURE 2, elements which have the same structure and serve the samepurpose as those shown in FIGURE l are given the same referencecharacter. In FIGURE 2 the disc 16 is rotated in the counter-clockwisedirection, as shown by the arrow 12, by a motor 14, through a variablespeed drive. The variable speed drive will be described later. Thedispensing apparatus 16 has an upper chamber 18 which is filled with theemulsion material. The ilow of the emulsion material from the upperchamber 18 is controlled by the valve 22. The dispensing apparatus 16 isrigidly supported by the upper and lower support varms 24 and 26 whichextend from the post 28. The emulsion material flows into the sphericalshell 32 which is flexibly supported from the lower support arrn 26 bythe member 30. The emulsion material 20 in the spherical shell 32 drainsthrough the opening 34 to coat the surface of the disc 10 along a spiralpath as shown by partial coating In FIGURE 2, the disc 10 is driven at achanging rate of revolution through an intermediate drive 50. Theintermediate drive 50 is shown in a schematic fashion, but it may be anyconventional type which produces a continuously controlled rotational`output with a -constant rotational input.

FIGURE 2 also includes an additional feature in that the dispensingapparatus 16 and spherical shell 32 move along a direct radial lineacross the surface of the disc 10 as opposed to the radial arc `ofFIGURE 1. The radial drive for the spherical shell 32 and dispensingapparatus 16 of FIGURE 2 is accomplished through the use of a screwdrive including a screw 58 which is threaded through a lower portion 60of the post 28. The screw S8 is driven in a counter-clockwise direction,as shown by the arrow 62, by the drive 50. The screw has a helicalthread which is designed to produce a spiral path of the spherical shell32 across the disc 10. For the particular embodiment of FIGURE 2 thespiral path has a constant spacing between adjacent turns along thespiral path.

As the spherical shell 32 moves across the disc 10, the emulsionmaterial 20 flows through the opening 34 and wets an area as defined bya meniscus ring surrounding, the contact point between the bottom of thespherical shell 32 and the surface of the disc 10. The spherical shell32, therefore, produces an even distribution of the emulsion material onthe surface of the disc 10, and, in addition, the spherical shell servesas a hydraulic lter to smooth the flow of the emulsion material from thedispensing apparatus 16. The disc 10 is driven by the motor 14 throughthe intermediate drive 50 so that the relative velocity between the disc10 and the spherical shell 32 is maintained at a constant value,notwithstanding the radial position of the spherical shell 32. Theconstant velocity relationship between the spherical shell and the disc10 provides that the unit area loading of the emulsion material on thesurface of the disc remains constant for all radial positions of thespherical shell.

In FIGURE 3, a detail view is shown of the relationship between thespherical shell 32 and the disc 10 of either FIGURE l or FIGURE 2 duringthe coating of the emulsion material 20 on the surface of the disc. Thesame reference characters are used as those for FIGURES l and 2. As canbe seen in FIGURE 3, the lower portion of the dispensing apparatus 161includes a tube which drops emulsion material 20 into the sphericalshell 32. It is desirable to have the emulsion material 20 build up ahead in the spherical shell 32 so that individual drops of emulsionmaterial from the dispensing apparatus 16 do not disturb the liow of theemulsion material out of the spherical shell 32. When the head ofemulsion material in the spherical shell 32 has a proper value, thespherical shell 32 operates as a lhydraulic filter so as to smooth theflow of the emulsion material from the dispensing apparatus 16.

The emulsion material 20 ows out of the spherical shell 32 through theopening 34. The size of the opening 34 is designed to produce thecorrect flow of emulsion material 20 in accordance with the desiredthickness of the coating of emulsion material on the surface of the disc10. The relative velocity and other factors between the spherical shell32 and the disc 10` are adjusted so as to produce the desired thicknessof emulsion material. As can be seen in FIGURE 3, as the emulsionmaterial flows from the spherical shell 32 through the opening 34, theemulsion material spreads over an area as defined by a meniscus ring 64.The meniscus ring, therefore, has

9 essentially a circular configuration, since it surrounds the contactpoint between the spherical shell 32 and the disc 10. The formation ofthe meniscus ring controls the distribution of the emulsion materialover a width equal to the diameter of the circular configuration of themeniscus ring. In this manner, the emulsion material is controlled to beevenly distributed over a localized area of the disc 10 and as the disc10 rotates relative to the spherical shell 32, a uniform coating of theemulsion material is produced on the surface of the disc 10. Theproduction of the meniscus ring around the bottom of the sphericalshell, therefore, controls the uniform distribution of the emulsionmaterial over a localized area.

Although FIGURES 1 and 2 illustrate the coating of the disc 10 startingat the outside of the disc and moving in toward the center of the disc,it may be desirable to reverse the above procedure and initiate thecoating of the disc 10 from the inside of the disc to the outside. Thismay be accomplished by merely reversing the drive to the dispensingapparatus 16 and the spherical shell 32. The coating of the disc 10 withemulsion material from the inside of the disc to the outside of the discmay have certain advantages over the systems shown in FIGURES 1 and 2.For example, as shown in FIGURE 4 wherein similar items have similarreference characters to those shown in FIGURES 1 and 2, a disc 10` isrotated by the motor 14 and the spherical shell 32 has produced auniform coating 46 on the surface of the disc 10.

In the recording systems which use discs coated with emulsion materialas shown in FIGURE 4, the inner portion of the emulsion coating is notusable. When the spherical shell 32 is producing the coating of emulsionmaterial at the inner portion of the disc 10, as shown by the portion66, the flow of emulsion material from the dispensing tank may beregulated so as to produce the desired uniformity. This can be seenwherein the characteristics of the coating 46 over the portion 66 isnon-uniform. Since the portion 66 is not used during recording, theadjustment of the flow of emulsion material would not produce anyadverse effects on the recording of information on the emulsion layer46. The coating apparatus of the invention is, therefore, adjusted toproduce a uniform coating over the remaining portion of the disc 10.

The coating of the disc with emulsion material from the inside o-f thedisc to the outside of the disc may also have an advantage in that it iseasier to remove the spherical shell from the sur-face of the discwithout disturbing the coating of emulsion material at the outside ofthe disc. For example, as the spherical shell 32 moves toward theoutside of the disc it may engage a separating platform 68 which gentlylifts the spherical shell away from the surface of the disc 10. If theflow of emulsion material to the spherical shell 32 is also shut off atthe proper time, the emulsion material within the spherical shell willcomplete the coating of the disc 10 at the same time as the sphericalshell reaches the outside edge of the disc. The separating platform 63would then lift the spherical shell slowly olf the rotating disc so thatthere is no sharp discontinuity in the coating of emulsion material andalso so that the coating of emulsion material is produced well to theedge of the disc 10l without running over the side of the disc 10.

In FIGURE 5, an embodiment of the invention is shown for producing acoating of emulsion material on a tape 100. The coating apparatus ofFIGURE includes a plurality of dispensing apparatus 102, 104 and 106which are similar to dispensing tank 16 of FIGURES 1 and 2. Thedispensing apparatus 102, 104 and 106 are all filled with emulsionmaterial 108 and the ow of the emulsion material 103 from the dispensingapparatus is controlled by valves 110, 112 and 114. The dispensingapparatus 102, 104 and 106 are supported above the tape 101i by upperand lower support arms 116 and 118 which extend between a pair of posts120 and 122. Posts 120 10 and 122 are maintained in a stationaryposition by support platforms 124 and 126.

A light trough structure 128 is supported by a pair of arms 130 and 132which extend from the posts 120 and 122. The trough 128` is supported soas to lightly contact the tape and so as to extend across the tape 100beneath the dispensing apparatus 102, 104 and 106. The trough has acylindrical bottom surface and endwalls 134 and 136 so as to retain theemulsion material 1018 owing into the trough 128. The emulsion material108 in the trough 128 flows through a slit 138i in the bottom of thetrough 128 so as to produce a coating 140 of emulsion material on thesurface of the tape 100. The tape 100 is moved in the direction as shownby the arrow 142 at a constant rate so as to produce the uniform coatingof emulsion material on the surface of the tape. It is to be appreciatedthat the slit 13S may be replaced by a plurality of separate openingssimilar to the openings 34 shown in FIGURES 1 and 2.

FIGURE 6 illustrates in more detail the relationship between the trough128 and the tape 100 of FIGURE 5. As shown in FIGURE 6, the emulsionmaterial 108 flows from the dispensing apparatus 102 and the otherdispensing apparatus into the trough 12S. In order to smooth out theflow of the emulsion material from the dispensing apparatus, it isdesirable to maintain a head of emulsion material within the trough 123.In this manner, the trough 128 acts as a hydraulic lter for the emulsionmaterial flow to the surface of the tape 100. The emulsion mate rial 108flows from the trough 128 through the slit 138 to the surface of thetape 100. The emulsion material llows between the bottom surface of thetrough and the tape until the adherence of the emulsion material issufcient to produce a pair of meniscuses 144 substantially parallelingthe line of contact between the bottom surface of the trough and thetape. The production of the pair of meniscuscs 144 controls the areaover which the emulsion material is distributed so as to provide for auniform distribution of the emulsion material on the surface of the tape100. The movement of the tape then provides a uniform coating 140 ofemulsion material on the -surface of the tape 100.

Although various embodiments of the invention have been shown whichillustrate different means for producing a uniform thin coating ofemulsion material on a substrate, it is to be appreciated that otheradaptations and modifications of the invention may be made. The invention, therefore, is only to be limited by the appended claims.

What is claimed is:

1. In an apparatus for producing a uniform coating of a coating materialon the surface of a substantially planar substrate,

a dispensing apparatus containing the coating material and includingmeans for directing the coating material toward the surface of thesubstantially planar substrate,

first means having a curved bottom lying on and con tacting the surfaceof the substantially planar substrate and having an upper areaoperatively coupled to the dispensing apparatus to store the coatingmaterial directed toward the surface of the substrate and having anopening extending from the upper area to the curved bottom of the firstmeans at a point other than any contact point between the curved bottomand the surface of the substantially planar substrate to produce auniform distribution. of the coating material on the surface of thesubstantially planar substrate over a local area by forming a meniscussurrounding the contact on the curved bottom of the first means, and

means for producing a relative movement between the rst means and thesubstrate to produce a coating of the coating material on the surface ofthe substantially planar substrate.

l l 2. The apparatus of claim 1 wherein the first means is a sphericalshell contacting the surface of the substrate at a single point andwherein the opening extends to the bottom surface of the shell at thepoint other than the contact point and wherein the meniscus forms :aring substantially centered around the contact point.

3. The apparatus of claim 1 wherein the rst means is a trough having acylindrical bottom surface contacting the surface of the substrate alonga line and wherein the opening extends to the bottom surface of thetrough away from the contact line and wherein the meniscus forms a pairof substantially parallel lines on either side of the contact line.

4. In an apparatus for producing a uniform coating of a coating materialon the surface of a disc,

a dispensing apparatus containing the coating material and includingmeans for directing the coating material toward the surface of the disc,

rst means lying on the surface of the disc and operatively coupled tothe dispensing tank to receive the coating material directed toward thesurface of the disc for smoothing the flow of the coating material fromthe dispensing apparatus and for producing a uniform distribution of thecoating material on the surface of the disc over a local area, and

means for producing a preprogramed relative movement between the firstmeans and the disc to produce a uniform coating of the coating materialon the surface of the disc.

5. In an apparatus for producing a uniform coating of a coating materialon the surface of a disc,

a dispensing apparatus containing the coating material and includingmeans for directing the coating material toward the surface of the disc,

first means having a curved bottom surface lying on the surface of thedisc and having an upper area operatively coupled to the dispensingapparatus to store the coating material directed toward the surface ofthe disc and having an opening extending from the upper area to thecurved bottom surface of the first means to produce a uniformdistribution of the coating material on the surface of the disc over alocal area by forming a meniscus on thc curved bottom surface of thefirst means,

second means operatively coupled to the disc to produce a preprogramedrotation of the disc, and

third means operatively coupled to the first means to produce apreprogramed radial motion of the first means across the surface of thedisc lfor uniformly coating the surface of the disc along a spiral path.

6. The apparatus of claim 5 wherein the first means is a sphericalshell.

7. The apparatus of claim 5 wherein the third means provides apreprogramed variation in the spacing between adjacent turns along thespiral path.

8. The apparatus of claim 5 wherein the second means provides apreprogramed variation in the speed of rotation of the disc.

9. In an apparatus for producing a uniform coating of a coating materialon the surface of a tape,

a dispensing apparatus containing the coating material and includingmeans for directing the coating material toward the surface of the tape,

first means having a curved bottom surface lying on and contacting thesurface of the tape and having an upper area operatively coupled to thedispensing apparatus to store the coating material directed toward thesurface of the tape and having an opening extending from the upper areato t-he curved bottom surface of the rst means away from the contactbetween the curved bottom and the surface of the tape to produce auniform distribution of the coating material on the surface of the tapeby forming a meniscus on the curved bottom surface of the rst meansaround the contact between the curved bottom and the surface of thetape, and

means operatively coupled to the tape for longitudinally moving the tapeto produce a coating of the coating material on the surface of the tape.

10. The apparatus of claim 9 wherein the first means is a troughextending across the tape.

11. In an apparatus for producing a uniform coating of a coatingmaterial on the surface of a substrate and having a dispensing apparatuscontaining the coating material and with the dispensing apparatusincluding means for directing the coating material toward the surface ofthe substrate,

a spherical shell having a curved bottom surface lying on the surface ofthe substrate and having an upper area to be operatively coupled to thedispensing tank for storing the coating material directed toward thesurface of the substrate and having an opening extending from the upperarea to the curved bottom surface for producing a uniform distributionof the coating material on the surface of the substrate over a localarea by forming a meniscus on the curved bottom surface.

References Cited UNITED STATES PATENTS 1,197,723 9/1916 Edison 118-3211,609,218 11/1926 Storck 118-401 2,167,727 8/1939 Rosebush 118-4012,179,221 11/1939 Schneider 118-218 2,961,821 11/1960 Marzocchi et al.118-401 X 3,201,275 8/1965 Herrick 118-401 X CHARLES A. VVLLMUTH,Primary Examiner.

R. I. SMITH, Assistant Examiner.

